To enhance an understanding of the physical and chemical characteristics of a wide variety of materials, surface analyses are often conducted. Typically, surface analysis techniques involve the characterization of the top 1.0-50.0 angstroms (.ANG.) of a solid. Although many techniques can be, and have been, used for surface characterization, four techniques have generally predominated. These are: X-Ray photoelectron spectroscopy (ESCA); Auger electron spectroscopy (AES); secondary ion mass spectroscopy (SIMS); and, low energy ion scattering spectrometry (ISS). These techniques are discussed briefly in: Hercules, D.M., Analytical Chemistry of Surfaces, Volume 58, No. 12, Oct. 1986, page 1177-1190, incorporated herein by reference.
Generally, the application of highly sensitive spectroscopic or spectrometric techniques are subject to operational limitations when applied to surface analyses. The surface being tested may be subject to interference by adventitious species. For example, water, hydrocarbons, fine dust particles etc. can become absorbed or adsorbed onto the surface being characterized, and interfere with the analysis. Also, damage, for example heat damage, to the surface being analyzed, for example by the spectroscopic probe, can introduce errors and/or artificial limitations. Further, if the surface being analyzed involves relatively short-lived species, decomposition or deterioration of the surface, prior to completion of analysis, can cause problems. This is a particular problem, for conventional systems, if the sample has to be transported from a location of preparation to an analysis lab.
Various techniques have been developed, to address some, or all, of the above concerns. Generally these have revolved around application of a variety of general methods, including: methods for cleaning a prepared sample surface prior to analysis; neutralizing surface charge to minimize errors in spectroscopy introduced by surface charge; and, methods for reduction of sample heating effects during analysis. Conventional cleaning techniques include sputter etching and sample heating to desorb contaminants. Conventional methods for reduction of heating effects include sample cooling and modifications of the excitation beam or probe.
Sputter etching is a well-known method of generating a clean surface, whereby a cathode, in vacuum, is energized to generate ions in the gas phase which impinge on the sputtered (sample) surface. This etches or cleans the sample surface. Sputter etching of a sample prior to analysis can effectively produce a surface without adventitious species. However, differential sputtering effects can cause a change in a composition of the test sample. Further, substantial undesired mixing effects of layers of the sample by knock-in can be brought about. In addition, the chemical reactivity of the surface of the sample may be affected. Also, without follow-up protection the surface may become damaged or contaminated.
Heating to remove volatile surface contaminants, prior to analysis, is helpful in some applications. However, some samples are not sufficiently thermally stable to withstand such treatments. Also, some surface contaminants are not sufficiently volatile to be easily removed by such techniques.
Surface neutralization techniques involve the bombardment of the sample surface with low energy electrons, to counteract any surface charges and enhance the analysis. In particular, this technique reduces spectral errors in charged particle spectroscopies. The technique, however, is often accompanied by inhomogeneous charging and subsequent spectral peak broadening, and thus is not completely effective. Techniques for measurement of surface charge, with correction for charging effects, require an assumption of uniform positive charging, and thus inherently involve limitations.
Sample cooling, to offset probe damage, has been somewhat effective in enhancing surface analyses. However, this technique requires a good thermal conductivity of the sample and a thermal contact to the cooling mechanism. In complicated, moderate to high vacuum arrangements, this may be difficult or expensive to achieve. Also, sample cooling may increase adsorption onto the sample surface of residual contaminants in the vacuum system.
Beam and probe modifications of certain surface analytical instruments, to achieve improvements, are also taught in the art. Beam filtering, for example, reduces X-ray damage in XPS, but it also severely reduces X-ray flux. Thus, a poorer signal to noise ratio results, and longer data acquisition time is necessitated. This can be a particular problem with short-lived films. Beam rastering and defocussing in AES has decreased, but has not eliminated, damage effects to the sample by diminishing the residence time of the beam on any particular sample spot or location.
When moderate to highly reactive sample surfaces are involved, for example a freshly deposited aluminum film, rapid contamination from residuals in the chamber will likely result, unless the sample is continuously maintained in ultra-high vacuum (approx. 10.sup.-10 torr.). Such a vacuum may be difficult to obtain and maintain in some systems, for example most vacuum deposition systems cannot readily achieve such low pressures. Also, the vapor pressures of same samples are too high to permit such a vacuum. Thus, it is desired, in many instances, that the sample be quickly removed from an environment of preparation or contamination, after generation. However, conventional methods and apparatuses have not readily accommodated this Generally, problems have concerned: maintenance of selected temperature, pressure and atmosphere; movement without substantial risk of surface damage; and, movement within a selected and preferably precisely controlled period of time.
At least one area in which sample movement systems have been developed for use in association with analytical devices is the field of providing for sample rotation to achieve an averaging in spectra. For example, a sample holder with a special mechanism enabling sample rotation during depth analysis by AES is described in: Zalar, A., Thin Solid Films, Volume 124, page 223-230 (1985) and Surface and Interface Analysis, Volume 9, page 41-46 (1986) incorporated herein by reference. Such sample handling systems do not readily lend assistance to the above described problems, since movement between regions of controlled, and often different, pressures, atmospheres and temperature are not readily achievable with them.
In general, what has been needed has been an apparatus and method for surface characterization which achieves improvement through a reduction in, and preferably a minimization of undesirable effects such as surface contamination and damage. Preferably, a system which readily accommodates the necessary and desirable temperature and pressure requirements for sample preparation, handling and characterization has been needed.